The goals of this project are to better understand the function of the hypothalamic-pituitary-thyroid system, how derangements in it are produced and how they result in abnormal function, and how such derangements can be recognized. Specific areas of current interest concern triiodothyronine and reverse-triiodothyronine physiology, the mechanisms of peripheral thyroxine deiodination to triiodothyronine and reverse triiodothyronine and their regulation, and the metabolic consequences of decreased extrathyroidal triiodothyronine production. Other studies in progress concern the physiology of thyroglobulin secretion and its relation to thyroid activation in hyperthyroid states and the physiology of hypothalamic and brain thyrotropin releasing hormone and its inactivation.